nl/mac80211: allow zero plink timeout to disable STA expiration

Both wpa_supplicant and mac80211 have and inactivity timer. By default
wpa_supplicant will be timed out in 5 minutes and mac80211's it is 30
minutes. If wpa_supplicant uses a longer timer than mac80211, it will
get unexpected disconnection by mac80211.

Using 0xffffffff instead as the configured value could solve this w/o
changing the code, but due to integer overflow in the expression used
this doesn't work. The expression is:

(current jiffies) > (frame Rx jiffies + NL80211_MESHCONF_PLINK_TIMEOUT * 250)

On 32bit system, the right side would overflow and be a very small
value if NL80211_MESHCONF_PLINK_TIMEOUT is sufficiently large,
causing unexpectedly early disconnections.

Instead allow disabling the inactivity timer to avoid this situation,
by passing the (previously invalid and useless) value 0.
Signed-off-by: Masashi Honma <masashi.honma@gmail.com>
[reword/rewrap commit log]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/uapi/linux/nl80211.h

@@ -3092,7 +3092,8 @@ enum nl80211_mesh_power_mode {
  *
  * @NL80211_MESHCONF_PLINK_TIMEOUT: If no tx activity is seen from a STA we've
  *	established peering with for longer than this time (in seconds), then
- *	remove it from the STA's list of peers.  Default is 30 minutes.
+ *	remove it from the STA's list of peers. You may set this to 0 to disable
+ *	the removal of the STA. Default is 30 minutes.
  *
  * @__NL80211_MESHCONF_ATTR_AFTER_LAST: internal use
  */

net/mac80211/mesh.c

@@ -574,6 +574,7 @@ static void ieee80211_mesh_housekeeping(struct ieee80211_sub_if_data *sdata)
 	struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
 	u32 changed;
 
+	if (ifmsh->mshcfg.plink_timeout > 0)
 		ieee80211_sta_expire(sdata, ifmsh->mshcfg.plink_timeout * HZ);
 	mesh_path_expire(sdata);
 

net/wireless/nl80211.c

@@ -5265,7 +5265,7 @@ do {									    \
 	FILL_IN_MESH_PARAM_IF_SET(tb, cfg, dot11MeshAwakeWindowDuration,
 				  0, 65535, mask,
 				  NL80211_MESHCONF_AWAKE_WINDOW, nla_get_u16);
-	FILL_IN_MESH_PARAM_IF_SET(tb, cfg, plink_timeout, 1, 0xffffffff,
+	FILL_IN_MESH_PARAM_IF_SET(tb, cfg, plink_timeout, 0, 0xffffffff,
 				  mask, NL80211_MESHCONF_PLINK_TIMEOUT,
 				  nla_get_u32);
 	if (mask_out)